Variable displacement systems work by selectively turning off cylinders in an engine, such as a bank of cylinders in a V-type engine. An example of a variable displacement system is the Multi-Displacement System (MDS) available from DaimlerChrysler Corp. of Auburn Hills, Mich. For example, a variable displacement system can deactivate three or four cylinders in a V6 or V8 engine, respectively, when the torque demand of the engine is relatively low. Advantageously, such variable displacement systems improve fuel economy in modern automobiles.
Disadvantageously, disturbances can arise from any high driveline torsional vibration levels, such as due to the cylinder deactivation in variable displacement system engines or aggressive lock-up strategies to improve fuel efficiency. These disturbances can potentially cause objectionable noise, vibration, and harshness (NVH) to automobile occupants. Modern automobiles utilize conservative calibrations for controlling slip in a launch device of a transmission, such as a torque converter, to prevent NVH from disturbing occupants. However, such conservative calibrations waste fuel. Modern automobiles do not currently employ direct feedback to control the slip in the launch device. A toque converter utilizes a torque converter lock-up clutch to prevent converter slip, however there currently does not exist a direct feedback system to control the lock-up clinch. For example, there are instances when a lightly-loaded powertrain running in third or fourth gear with a locked torque converter at 1000 revolutions-per-minute (rpm) performs without objectionable NVH. However because some road conditions (e.g., a slight uphill grade) may induce disturbances, a locked-up converter during cylinder reduced operation at 1000 rpm in these gears cannot be permitted for fear of NVH.